In place of hydrocarbons as a source of energy to generate power, hydrogen has been suggested as being a more beneficial alternative. Hydrogen gas can generate more power per gram and emit less, or even no, exhaust pollutants into the atmosphere. However, the problem of using hydrogen as a power source is its difficulty to store, especially in on-off mobile applications.
Hydrogen gas can be stored at high pressures in thick walled vessels on-board a motorized vehicle. These vessels are heavy, and high pressure is a concern. Metal hydrides, MHx, contain thermally releasable hydrogen, but only in small, inefficient amounts. Lithium and sodium borohydrides contain a higher proportion of hydrogen that can be released by hydrolysis. But this approach, too, is an engineering challenge.
In U.S. Pat. No. 5,372,617, Kerrebrock, et al., water is added to pelletized or granular hydride particles in a pressurizable reaction chamber vessel upon demand for hydrogen gas from a fuel cell. The system is used to power a submersible vessel and is intended for generally continuous operation for the duration of the task of the undersea vehicle. Lithium borohydride, for example, and water react to form hydrogen and solid by-products. The addition of water is used to control the supply of hydrogen gas to the fuel cell. Solid by-products formed during hydrolysis are retained in or returned to the hydride storage portion of the system. This practice impedes further reaction of water with unreacted hydride. Furthermore, the practice relies on continuous operation at an elevated temperature to avoid water consumption as hydrates. The Kerrebrock, et al process is not useful in applications like automotive vehicles requiring go and stop operation.
Thus, it is an object of the present invention to provide a hydrogen generation system suitable for start and stop vehicle operation. Hydrogen containing particles and water are stored separately until needed. They must then be supplied to a suitable hydrolysis reactor in chemically balanced proportions. Since the water reacts at the surfaces of the hydride particles to form a solid by-product in addition to hydrogen gas, the reactor must be adapted to break off and move the solid by-products, facilitating the reaction and the removal of by products. It is a further object of the present invention to provide a hydrogen generation system that is compact and requires a minimal amount of power consuming equipment.